Yes, low bieuret urea will help. Phosphates not that much crucial though. Better if you find fertilizer with minors that include Mg, Zn, Fe, etc.
Over here, we could not easily find urea from stores. Ammonium suphate is the cheapest one. I mix this with triple 16 and Epsom salt (magnesium sulfate hydrate). Then also topdress with steer manure for other minor minerals. I use ratio of 1 cup Ammonium sulfate, 1/2 cup 16-16-16, and 1/8 cup Epsom salt. Get a 5-gallon pail, dissolve the 1/2 cup of triple 16 in 1 gallon hot water from kitchen faucet, stir vigorously, then add 1 gallon of water, 1 cup of ammonium sulfate, 1/8 cup of epsom salt, stir again to dissolve fertilizer, and fill in the rest of the pail with water to 4 gallon level (or just comfortably so that it won't spill when you carry the pail), and spread the solution around the dripline of the citrus tree. Use about 1/2 gallon of solution per inch diameter of tree per month.
